PROBLEMS OF INORGANIC CHEMISTRY. 39 



(CoCl 4 )". And what holds for cobalt chloride also undoubtedly holds 

 for many similar compounds. 



In determining the constitution of the compounds of carbon, stereo- 

 chemistry has played a great part. The ordinary structural formulae 

 are now universally acknowledged to be only pictorial, if, indeed, that 

 word is legitimate; perhaps it would be better to say that they are dis- 

 torted attempts at pictures, the drawing of which is entirely free from 

 all rules of perspective. But these formulae may in almost every case 

 be made nearly true pictures of the configuration of the molecules. The 

 benzine formula, to choose an instance which is by no means the sim- 

 plest, has been shown by Collie to be imitated by a model which repre- 

 sents in an unstrained manner the behavior of that body on treatment 

 with reagents. But in the domain of inorganic chemistry, little prog- 

 ress has been made. Some ingenious ideas of the geologist Sollas on 

 this problem have hardly received the attention which they deserve; 

 perhaps they may have been regarded as too speculative. On the other 

 hand, Le Bel's and Pope's proof of the stereo-isomerism of certain com- 

 pounds of nitrogen; Pope's demonstration of the tetrahedral structure 

 of the alkyl derivatives of tin; and Smiles's syntheses of stereo- 

 isomeric sulphur compounds give us the hope that further investigation 

 will lead to the classification of many other elements from this point 

 of view. Indeed, the field is almost virgin soil; but it is well worth 

 while cultivating. There is no doubt that the investigation of other 

 organo-metallic compounds will result in the discovery of stereo- 

 isomerides ; yet the methods of investigation capable of separating such 

 constituents have in most cases still to be discovered. 



The number of chemical isomerides among inorganic compounds is 

 a restricted one. Werner has done much to elucidate this subject in 

 the case of complex ammonia derivatives of metals and their salts; 

 but there appears to be little doubt that if looked for, the same or 

 similar phenomena would be discoverable in compounds with much 

 simpler formulas. The two forms of So 3 , sulphuric anhydride, are an 

 instance in point. No doubt formation under different conditions of 

 temperature and pressure might result in the greater stability of some 

 forms which under our ordinary conditions are changeable and unstable. 

 The fact that under higher pressures than are generally at our disposal 

 different forms of ice have been proved to exist, and the application 

 of the phase-rule to such cases, will greatly enlarge our knowledge of 

 molecular isomerism. 



The phenomena of catalysis have been extensively studied of recent 

 years, and have obviously an important bearing on such problems. A 

 catalytic agent is one which accelerates or retards the velocity of re- 

 action. Without inquiring into the mechanism of catalysis, its exist- 

 ence may be made to influence the rate of chemical change, and to 

 render stable bodies which under ordinary conditions are unstable. For 

 if it is possible to accelerate a chemical change in such a way that the 



